LiFePO4 vs Lead Acid a cost analysis for energy storage.

[russ]

I do not sell a product there is no profit from my Open Source solar BMS. But I'm also busy with the Kickstarter campaign so I will be glad to take a break from this discussion.

Good -

[electrodacus]

I am done with you. Not worth my time. You are selling a product, I am not.

I do not sell a product there is no profit from my Open Source solar BMS. But I'm also busy with the Kickstarter campaign so I will be glad to take a break from this discussion.

[electrodacus]

It proves that you don't really understand the workings or advantages of MPPT.
Try reading the stickies here about them. In order to get the greatest harvest from them the Vmp of the panels has to be about 50% higher than the battery voltage.
And your cost per watt is way off for the PV.
Here is an example
100 Watt 36 cell panel VMP of 17.
Imp of 5.9

Charging a 12V battery you are only getting 70 watts into the battery. A loss of 30%
Go to Mppt and you get upwards of 95 watts into the battery. A loss of 5%
OH and you can't series the panels to reduce wire size or compensate for long runs from panels to controller with PWM or the losses get worse.
On a 100 watt system it probably doesn't make much difference but get over 200 watts and it makes a big difference.

I will try to answerer all your questions if I can.

I promise I understand how an MPPT works in the most intimate detail. I used to design DC-DC converter. And I also understand the algorithm part of an MPPT.
Small offgrid panels use 36 cells for 12V and 72cells for 24V battery that is to be able to compensate for high temperatures in hot climates.
Mppt will be most effective in cold and sunny days and not as effective in hot summer days. With a 36 cell panel and 12V Lead Acid battery the average gain over a year compared with an PWM controller is not higher than 15% will wary a bit with location (climate).
Those 15% can be also obtain using a simpler and less expensive PWM controller and a solar PV panel that is 15% larger.
Notice I use % so the size of the system is irrelevant. A larger MPPT controller will also be more expensive.
How is 1$/Watt way off for solar PV panels ? Maybe very small solar panels cost a bit more but I think 1$/Watt is a good average price for PV panels.

As for your example 100W panel example

A 12V battery dose not usually have 12V during charging it will be quite a bit more (13 to 14.4V) depending on the charge rate and SOC of the battery.
Also that 17V at max power point is calculated for cells with 25C temperature it will be quite a bit lower in the summer.

For small offgrid systems you usually have the panels quite close to the controller and batteries (usually mounted on the roof or somewhere quite close) so there are almost no savings on copper. Plus at high voltage difference between PV and battery the MPPT (DC-DC converter) will get quite inefficient dissipating even more heat and reducing the life of the MPPT controller even more (mostly the electrolysis will fail).
An PWM dose not get that hot and it dose not need electrolytic so it can last as much as the solar panels over 25 years where MPPT will be changed quite a few times adding to the cost of operation.

[Sunking]

Of course that premium Trojan battery was not the best battery in the market but what I calculated was cost / kWh stored.
So let see how much better is this Rolls 5000 series I have no idea but I will calculate just now.
I found this 6-CS-25PS from the 5000 series at 1235$ seems to be the best price (some say retail is over 2000$ but that is advertising I think)
This has 681Ah at C 1/10 so using the same formula from my table 6x681Ah = 4086Wh x 1500 cycles 100% DOD = 6129kWh then 1235$/6129kWh = 20cent/kWh I think that is almost the same as Trojan premium or quite close is like they make the reverse calculation when they set the price for this batteries.
Anyway is not a better value for money that the Trojan Premium and is probably worse since you will need to use this at higher rate to be able to make use of the entire capacity over the 10 - 15 years amortisation period.
You will need to discharge this in average to 50% every day to get the benefit of higher cycles over 10 years amortisation and if you discharge this at high rate you will have way less capacity is not as LiFePO4 where 1C discharge is vs C 1/10 makes no difference.

I am done with you. Not worth my time. You are selling a product, I am not.

[electrodacus]

OK that is what happens when you are a 1 Trick Pony.

Rolls Battery 1500 cycles with 5000 series at 100% DOD. At 50% DOD greater than 3000 cycles. Over 5000 cyles @ the dsigned 20% DOD. With LFP you have a Boat Anchor @ 100% DOD and around 2000 between the sheets. Rolls Kwh 5000 series cost are 1/3 to 1/5 of all LFP....................

Any questions?

Me thinks I am done here. How about you?

Of course that premium Trojan battery was not the best battery in the market but what I calculated was cost / kWh stored.
So let see how much better is this Rolls 5000 series I have no idea but I will calculate just now.
I found this 6-CS-25PS from the 5000 series at 1235$ seems to be the best price (some say retail is over 2000$ but that is advertising I think)
This has 681Ah at C 1/10 so using the same formula from my table 6x681Ah = 4086Wh x 1500 cycles 100% DOD = 6129kWh then 1235$/6129kWh = 20cent/kWh I think that is almost the same as Trojan premium or quite close is like they make the reverse calculation when they set the price for this batteries.
Anyway is not a better value for money that the Trojan Premium and is probably worse since you will need to use this at higher rate to be able to make use of the entire capacity over the 10 - 15 years amortisation period.
You will need to discharge this in average to 50% every day to get the benefit of higher cycles over 10 years amortisation and if you discharge this at high rate you will have way less capacity is not as LiFePO4 where 1C discharge is vs C 1/10 makes no difference.

[Sunking]

It proves that you don't really understand the workings or advantages of MPPT.

brother.

PWM charge current out = Current In = Current Out. (A PWM controller is a SERIES REGULATOR)
MPPT charge current out = Panel Wattage / Nominal Battery Voltage. (A MPPT controller is a simple buck/boost switch mode DC-DC Converter like an AC transformer with very small power loss). Something a 2nd year engineer student will understand.

Simple 5th grade math for a train driver.

[Naptown]

Can you elaborate?

It proves that you don't really understand the workings or advantages of MPPT.
Try reading the stickies here about them. In order to get the greatest harvest from them the Vmp of the panels has to be about 50% higher than the battery voltage.
And your cost per watt is way off for the PV.
Here is an example
100 Watt 36 cell panel VMP of 17.
Imp of 5.9

Charging a 12V battery you are only getting 70 watts into the battery. A loss of 30%
Go to Mppt and you get upwards of 95 watts into the battery. A loss of 5%
OH and you can't series the panels to reduce wire size or compensate for long runs from panels to controller with PWM or the losses get worse.
On a 100 watt system it probably doesn't make much difference but get over 200 watts and it makes a big difference.

[Sunking]

LiFePO4 in all specs I seen are tests at either 100% DOD or 80% DOD (from 100% SOC down to 20% SOC) and they last min 2000 and up to 3000 cycles depending on manufacturer and quality of the cell.

OK that is what happens when you are a 1 Trick Pony.

Rolls Battery 1500 cycles with 5000 series at 100% DOD. At 50% DOD greater than 3000 cycles. Over 5000 cyles @ the designed 20% DOD. With LFP you have a Boat Anchor @ 100% DOD and around 2000 between the sheets. Rolls Kwh 5000 series cost are 1/3 to 1/5 of all LFP.................... You do not have to be an engineer or accountant to understand facts.

Any questions?

Me thinks I am done here. How about you?

[electrodacus]

I agree and that is what I have been pounding for many days. Any Lithium chemistry operates best at 20 to 80% SOC. FLA is best between 50 to 100% SOC. Lithium has a 60% usable capacity and FLA has 50% usable. Not much difference when you compare Apples to Apples. A 1Kwh/day 12 volt FLA battery with 3 day real Autonomy 500 AH and a LFP is 400 AH. Buy both in High End manufactures gets you around 2000 real life cycles. Differenc is th eLFP cost around $4500 plus BMS and interconnect busswork and FLA cost $1400. No contest.

It is like seeing two gas stations next door to each other. One sells gas for $3/gal, the other sells for $12/gal. What person buys gas for $12/gal if given the choice? I guess you by the $12/gal gas huh?

First Lithium batteries are so different that you can not use general therm.
Second is true that all Lithium Batteries prefer to be in the middle of the SOC but they are never used that way in any application.
LiFePO4 in all specs I seen are tests at either 100% DOD or 80% DOD (from 100% SOC down to 20% SOC) and they last min 2000 and up to 3000 cycles depending on manufacturer and quality of the cell.
One LiFePO4 manufacturer specified 2000 cycles for 80% DOD and 3500cycles for 70% DOD.
Lead Acid manufacturers suggest only an average of 20% DOD for offgrid solar energy storage so that the battery can last a few years.

I will not recommend tiring to design a battery bank for more than 10 years no matter the type of battery Lead Acid or LiFePO4
In this case you do not care how deep you discharge a LiFePO4 can be 5% to 95% and will still last those 10 years.

My installation is a good example I use a 24V 100A battery (2.5kWh total capacity at least 2kWh usable) with an average usage of 2.5kWh/day as low as 2kWh/day in winter and about 3kWh/day the rest of the year.
I have a 720W of solar PV panels that produce 60kWh/month in the worst month December and over 100kWh/month in the other 3 seasons + a small 300W wind turbine that I only use in some days manually at the moment most of the time is with electromagnetic break ON.
When I was thinking on Lead Acid I was looking at a batter of at least 24V 300Ah C/20.
My GBS 24V 100A battery was 1200$ I think is around 1000 or 1100$ now but there is so much more choice so I do not make any recommendations.
Once the Solar BMS is installed I have no worries or additional work.
I have done a charge discharge cycle when I got the GBS battery two years ago is on my youtube channel and I will do this spring another test to see how much has the battery degraded with 1 year of storage and one year of heavy use on my offgrid house.

[electrodacus]

" better to remain silent and be thought a fool than to open it and remove all doubt.
Benjamin Franklin IIRC

That post proves that you know very little.

Can you elaborate?

[Sunking]

"Li-ion does not need to be fully charged, as is the case with lead acid, nor is it desirable to do so. In fact, it is better not to fully charge, because high voltages stresses the battery. Choosing a lower voltage threshold, or eliminating the saturation charge altogether, prolongs battery life but this reduces the runtime."

I agree and that is what I have been pounding for many days. Any Lithium chemistry operates best at 20 to 80% SOC. FLA is best between 50 to 100% SOC. Lithium has a 60% usable capacity and FLA has 50% usable. Not much difference when you compare Apples to Apples. A 1Kwh/day 12 volt FLA battery with 3 day real Autonomy 500 AH and a LFP is 400 AH. Buy both in High End manufactures gets you around 2000 real life cycles. Differenc is th eLFP cost around $4500 plus BMS and interconnect busswork and FLA cost $1400. No contest.

It is like seeing two gas stations next door to each other. One sells gas for $3/gal, the other sells for $12/gal. What person buys gas for $12/gal if given the choice? I guess you by the $12/gal gas huh?

[Naptown]

Thanks for asking. There is no replacement is just obsolete for Lead Acid use the inexpensive and long lasting PWM controllers.
The reason is obsolete has to do with cost again
Say you need 1000W of solar panels (just a number can be 50W) and you want to get the best out of them using an MPPT depending on climate and location you may get an additional 10 to 15% energy in average using an MPPT but you can also get the same by buying 10 to 15% more panels that will cost at 1$/watt around 100 to 150$ more. So now the MPPT needs to compete with that and is impossible to do so since a 1000W DC-DC converter the main part in a MPPT will cost more than that and will need replacement every 5 years so you need about 5 during the life time of the panels.
MPPT barely made sense at 5$/Watt solar PV panels but is quite impossible to find a reason for it at 1$/Watt
Same is true for the solar tracking is obsolete for the same reason it makes no economic sense.

" better to remain silent and be thought a fool than to open it and remove all doubt.
Benjamin Franklin IIRC

That post proves that you know very little.

[Sunking]

When you size a battery you need to take in to account battery efficiency. Maybe it can be overlooked for a battery with 95% efficiency but not for one with 75% or less.

Incorrect again. To determine panel wattage required to replace energy used one has to apply a correction factor to account for charge losses. This depends on battery chemistry like Lead Acid (and it directives like AGM which is more efficient) NiCd, NiFe, or your favorite LFP. Correction factor is a number greater than 1 (ONE). For a FLA system using MPPT the CF is 1.5, for PWM and FLA is 2, and for LFP using MPPT will be 1.2. So yes LFP has a higher charge efficiency bu twhen it comes to dollar and cents it is less expensive to use a higher panel wattage than 4 x lithium battery cost.

For example if you need 1 Kwh per day:

• A FLA MPPT system needs to generate 1.5 Kwh at the panels:

• A FLA PWM system 2 Kwh
• A LFP MPPT 1.2 Kwh

So if you have a winter Solar Insolation of 3 Sun Hours you need a panel wattage of

FLA w MPPT = 500 watts.
FLA w PWM = 750 watts
LFP w MPPT = 400 watts.

Using GT panels we are talking about $100 difference in price and panels last a long time of 20 years. But when we look at Battery Cost and life expectancy of 5 years which is about all you are going to get out of either LFP or FLA we have a 300% to 500% difference in price. To make both systems equal with 3 days of real autonomy with a 12 volt system it takes a 500 AH FLA battery and a 350 to 400 AH LFP battery. That 500 AH Rolls 5000 series battery cost roughly $1400, and a 400 AH LFP battery cost roughly $4500 to $5000 plus a BMS, and fabricated buss work which I will not go into because it is a moot point with added cost.

You do not have to be an accountant to figure out economics. You do not have to be a train driver (engineer) to figure out using LFP will be more complex and expensive using 16 LFP cells plus BMS, racking, and interconnect buss. Vs 2 6-volt FLA cells with a single #6 AWG copper wire interconnect. KISS it. (Keep It Simple Stupid)

[electrodacus]

If MPPT is obsolete, what has replaced it ? Inquiring minds want to know.

Thanks for asking. There is no replacement is just obsolete for Lead Acid use the inexpensive and long lasting PWM controllers.
The reason is obsolete has to do with cost again
Say you need 1000W of solar panels (just a number can be 50W) and you want to get the best out of them using an MPPT depending on climate and location you may get an additional 10 to 15% energy in average using an MPPT but you can also get the same by buying 10 to 15% more panels that will cost at 1$/watt around 100 to 150$ more. So now the MPPT needs to compete with that and is impossible to do so since a 1000W DC-DC converter the main part in a MPPT will cost more than that and will need replacement every 5 years so you need about 5 during the life time of the panels.
MPPT barely made sense at 5$/Watt solar PV panels but is quite impossible to find a reason for it at 1$/Watt
Same is true for the solar tracking is obsolete for the same reason it makes no economic sense.

[Mike90250]

I did not wanted to mention MPPT since that is an obsolete technology at 1$/Watt for solar PV The idea was that it can not use the total PV power even when Battery is not full. ....

If MPPT is obsolete, what has replaced it ? Inquiring minds want to know.